Weird! Our Universe May Be a 'Multiverse,' Scientists Say

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Is our universe just one of many? While the concept is bizarre,
it's a real possibility, according to scientists who have devised
the first test to investigate the idea.

The potential that we live in a multiverse arises from a theory
called eternal inflation, which posits that
shortly after the Big Bang that formed the universe,
space-time expanded at different rates in different places,
giving rise to bubble universes that may function with their own
separate laws of physics.

The idea has seemed purely hypothetical, until now. In a new
study, researchers suggest that if our universe has siblings, we
may have bumped into them. Such collisions would have left
lasting marks in the cosmic microwave background (CMB) radiation,
the diffuse light left over from the Big Bang that pervades the
universe, the researchers say.

"It brings the idea of eternal inflation and bubble collisions
into the realm of testable science," said research team member
Daniel Mortlock, an astrophysicist at Imperial College London.
"If it's not testable, it's hard to even call it science."
[ Video: How to
Remake the Big Bang ]

Universes going bump in the night

Mortlock and the team, led by graduate student Stephen Feeney of
University College London, searched the best available
observations of the cosmic microwave background for signs of
bubble universe collisions, but didn't find anything conclusive.
If two universes had collided, the researchers say, it would have
left a circular pattern behind in the cosmic microwave
background.

"If you imagine two ordinary soap bubbles colliding, then the
surface where they intersect is going to be a circle, so that's
the key signature we're looking for in the CMB," Mortlock told
SPACE.com. "It's not any old perturbation, it's circular and it's
got a particular type of profile. There's no obvious sort of
other thing that could cause this."

The researchers developed a computer algorithm to analyze
CMB observations for patterns that would fit. In data from NASA's
Wilkinson Microwave Anisotropy Probe (WMAP), the program found
four regions in the universe that were flagged as promising.
However, statistical analyses suggested these patterns were
likely to be random, resembling the circular shapes of collisions
simply by coincidence.

Data from the European
Space Agency's Planck satellite, which launched in 2009, are
expected to be far more detailed than those from WMAP. The Planck
measurements are set to be released in 2013, and the researchers
plan to look again, surveying in particular the four areas of
interest from this study.

"I think the Feeney et al. paper is a great first step in trying
to seriously look for signals of cosmological bubble collisions,"
said astrophysicist Thomas Levi of the University of British
Columbia in Canada, who was not involved in the study. "While I
believe the potential exists to detect the presence of other
universes, the present data from WMAP is not likely to be precise
enough to make a definitive statement. We will have to wait for
data from future CMB experiments, such as the Planck satellite.
The next few years could be quite exciting."

The universe that's 'just right'

The idea of other
universes out there is mind-bending, but scientists say
in some ways it actually makes sense.

"It helps explain some of the strange coincidences about our own
universe," Mortlock said. "Why is our universe so amenable to
life?"

Many of the fundamental constants in our universe, such as the
strength of gravity and the speed of light, seem perfectly
calibrated to produce a universe in which galaxies, stars,
planets and even life can form. If any of these constants had
been tweaked at all, the universe would likely be empty, with no
stars and no life.

"One possibility is there are multiple different universes with
different laws, and some are not right for life and so life
doesn't evolve, and some are right for life and so creatures
evolve and make measurements and ask deep, twisty questions like
this," Mortlock said. "For that reason [the theory] is very
appealing."

However, the possibility of multiple universes also comes with
some unsettling implications. For example, some calculations
suggest that a reality with infinite space and infinite universes
would necessarily have to repeat itself sometimes, leading to the
conclusion that copies of Earth and everyone on it exist
somewhere else out there.

"Once you open up this can of worms, there's all sorts of very
adventurous thinking on this sort of thing," Mortlock said. "If
there's infinitely many universes, then surely there are other
copies of you and me having this conversation. It's hard to think
about, but it's hard to get around."

The scientists detailed their study in two research papers
published recently in the journals Physical Review
Letters and Physical Review D.